All materials in use as blood contact surfaces for cardiovascular materials are thrombogenic. Tissue cultured endothelial cells may provide a thromboresistant prosthetic surface, however, technical problems associated with cultured linings preclude their clinical application. One of the greatest of these problems is adherence of the in vitro cultured cells after implantation in the blood stream. Adherence of the cells is prerequisite to their success as a thromboresistant lining. We know from in vivo experiments that it is not feasible to determine whether cultured cells remain adherent after blood contact because of thrombus formation. In an in vitro mock circulatory loop, we propose to study the effects of physiological flow and pressure on cultured cells, thus separating the variables of flow from the complex thrombus-forming elements of the blood. The cells to be studied are endothelial cells cultured from the bovine aorta, the human umbilical vein, and the human saphenous vein. Our objectives are to determine (1) the effects of flow on cell cultured surfaces, (2) the effects of flow on propagation of cultured cells, (3) morphological changes resulting from flow as assessed by scanning and transmission electron microscopy, (4) the influence of the topography of the cell culture substrate, and (5) compare results obtained with cultured bovine endothelial cells to those obtained with cultured human endothelial cells. We hope to provide a better technique for cell-culturing prosthetic surfaces for blood contact such that clinical application of this technique becomes feasible. Moreover, we hope to develop an in vitro system which will serve as a model for controlled studies for disease processes of the vessel wall.